The Lost Emperor: A Colony of Penguins Disappears

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A small colony of emperor penguins on an island off the West
Antarctic Peninsula is gone, and the most likely culprit is loss
of sea ice caused by warming. Although it has been predicted that
penguins could suffer greatly because of global warming, this is
the first time the disappearance of a colony has been documented.

The researchers, however, caution that their study is hampered by
a lack of long-term information on
emperor penguins, both at this site and in general, and their
environment.

Emperor penguins are regal, if bulky, birds that stand as high as
4 feet (1.2 meters) and can weigh as much as 84 pounds (38
kilograms). This colony, first spotted in 1948 on an island
dubbed Emperor Island, was a small one that had approximately 150
breeding pairs.

Observations are spotty, but the populations appear to have been
relatively stable until the 1970s. A report in 1978 showed a
sharp drop in population, a trend that continued until an
airplane survey found the island empty in 2009. [ Album:
Life at the South Pole ]

This raises the question: Did the penguins die off or just
relocate? "That's one of the big unknowns," said Philip Trathan,
the lead researcher and head of conservation biology at the
British Antarctic Survey.

Penguin habits

Emperor penguins appear to return home each year to the site
where they hatched. But the colonies must sometimes relocate
because of changes in the ice, however, the details of how this
happens aren't understood. Trathan and his colleagues speculate
that the Emperor Island penguins born in the late 1970s – they
live to be about 20 years old – may have continued to return in
smaller numbers each year until the colony disappeared.

Ice is crucial to these birds. Most emperor
penguins breed on sea ice — called fast ice — which attaches
to the ice shelves and coastlines, and does not move in wind or
currents. As the ice develops in autumn, the birds gather at
their colonies. They remain there, mating, laying eggs and
raising chicks until mid-summer, when the chicks fledge and the
fast ice breaks up. They also forage within the pack ice, which
floats at the surface of the water.

The colony on Emperor Island frequently nested on land, although
reports also show these birds setting up house on the ice. So,
the disappearance of this colony indicates that breeding on land
may not be a good alternative, Trathan said.

Caused by climate change?

The cause of the disappearance is not clear-cut, but the evidence
indicates a connection to climate change.

"The one site in Antarctica where we have seen really big changes
is the West Antarctic Peninsula," Trathan said. For much of the
20th century, this region has warmed at an unprecedented rate,
particularly in recent decades, the researchers write in a study
published Feb. 28 in the journal PLoS ONE.

Data collected from a station about 25 miles (40 kilometers) away
shows a marked increase in air temperature; meanwhile, the local
sea ice in the area has been forming later and melting earlier.
One study published in 2007 in the Journal of Geophysical
Research found that between 1979 and 2004 in this region, sea ice
began advancing about 54 days later and retreating 31 days
earlier. ( This
trend does not hold for all of Antarctic waters, but,
ultimately, Antarctic sea ice is expected to shrink
significantly.)

In addition to destroying colony habitat, warming and
the loss of sea ice could indirectly affect the penguins by
reducing the availability of the fish, krill and squid they eat,
or by increasing the presence of predators, such as giant
petrels, the authors write.

Climate change is not a new culprit. A previous modeling study
projected that global warming would be very bad for emperor
penguins. Published in the journal the Proceedings of the
National Academy of Sciences in 2009, the study found a 36
percent chance that shrinking Antarctic sea ice could cause
emperor penguin populations to drop by 95 percent or more by
2100.

It's possible that factors including disease or extreme weather
may have caused this particular colony to disappear, but there is
no data available to test these hypotheses, Trathan said.

"We need to look at more colonies so we can reduce the
uncertainty," he said. "With the first report, there is a high
degree of uncertainty."